Titanium tungsten alloys produced by additions of tungsten nanopowder

ABSTRACT

Disclosed herein are titanium-tungsten alloys and composites wherein the tungsten comprises 0.5% to 40% by weight of the alloy. Also disclosed is a method of making such alloys and composites using powders of tungsten less then 3 μm in size, such as 1 μm or less. Also disclosed is a method of making the titanium alloy by powder metallurgy, and products made from such alloys or billets that may be cast, forged, or extruded. These methods of production can be used to make titanium alloys comprising other slow-diffusing beta stabilizers, such as but not limited to V, Nb, Mo, and Ta.

This application claims the benefit of domestic priority to U.S.Provisional Patent Application Ser. No. 60/563,009, filed Apr. 19, 2004,which is herein incorporated by reference in its entirety.

Disclosed herein are titanium-tungsten alloys and composites. Alsodisclosed is a method of making such alloys and composites usingnanopowders of tungsten and optionally comprising slow-diffusing betastabilizers, such as but not limited to V, Nb, Mo, and Ta.

While Ti alloys strengthened by W are generally desirable because theyare strong wear resistant alloys, such alloys are difficult, if notimpossible, to prepare by typical techniques. For example, in a castingprocess, W generally completely dissolves in the molten Ti during themelting step. As the resulting ingot solidifies beta-rich large,elongated islands form between the dendrites of the solidified casting.These resulting defects lead to poor mechanical properties in the finalproduct.

Until the present disclosure, the preparation of Ti—W by powdermetallurgy (PIM), was not commercially viable because of the highmelting point and slow diffusivity associated with W that causes it toremain segregated as discrete or undissolved particles. Ti—W alloys arementioned in the literature for use as sputtering targets and in thinfilm applications; however, these alloys are tungsten (W) based withtypically 10% or less Ti.

Literature that does describe Ti based alloys comprising W describes Wbeing added to form a particulate dispersion. For example, M. Frary, S.M. Abkowitz, and D. C. Dunand, “Microstructure and Mechanical Propertiesof Ti/W and Ti-6Al-4V/W Composites Fabricated by Powder-Metallurgy,”Materials Science and Engineering A344 (2003) 103-112, which is hereinincorporated by reference, shows that partially diffused W dispersionsin Ti powder (Commercially Pure “CP” Ti) and Ti-based alloys (Ti-6Al-4V)increases strength with an acceptable loss in ductility. The alloysdescribed in Frary et al. comprise 3 μm to 10 μm tungsten powders thatare too large to completely diffuse.

SUMMARY OF THE INVENTION

The present disclosure avoids the aforementioned problems by usingtungsten nanopowder. As used herein, nanopowder is defined as powdersless than 1 micron, such as powders ranging from about 8 angstroms (thedetection limit of electron microscopy) to less than 1 micron. TheInventors have discovered that the use of W nanopowder in thepreparation of Ti—W alloys allows the W to completely diffuse into theTi matrix during a typical P/M sintering cycle.

In one embodiment, completely diffused W nanopowder forms an alpha/betaor all beta microstructure, or as alpha/beta or all beta microstructurecontaining a dispersion described as “beta phase islands.” Beta phaseislands are a microscopic beta rich structure dispersed throughout analpha, alpha/beta or all-beta microstructure. These dispersions resultin Ti/W alloys with properties that are superior to a dispersion ofpartially diffused W particulates produced using Ti powder 3 μm orlarger. In fact, the commercially pure (CP) Ti with 10% W containingdispersions of beta phase islands can have properties superior toTi-6Al-4V. In addition, the Ti-6Al-4V with 10% W can have annealedproperties equivalent to the highly alloyed all-beta alloys that requiresolution treatment and aging to fully develop their properties (e.g.Ti-13V-11Cr-3Al).

In accordance with the present disclosure, W nanopowder can be blendedwith CP (commercially pure) Ti powder and, in the case of an alloy,blended with Ti powder, other elemental powders or with master alloypowders, which is defined as the mixture of starting metal powders usedto form the resulting alloy by powder metallurgy processing. The powderblend is compacted, sintered and may or may not be hot isostaticpressed. The product may be subjected to additional processing, such as,forging, casting, or extrusion.

A casting billet may also be prepared in the manner described above andthen cast to shape. Ti—W master alloy additions can also be prepared bythe methods disclosed in this invention. These master alloy additionscan be used in casting of Ti—W or may be made into master alloy powderby attrition for use in P/M processing.

The total diffusion of W, as disclosed herein, results in an alpha/betaphase microstructure in CP titanium typical of commercial alpha/betaalloys. In alpha/beta alloys the total diffusion of W results in a nearbeta or all beta microstructure. The Ti—W alloys also have propertiesthat are superior to conventional Ti-6Al-4V. Further the Ti—W alpha/betaand all-beta alloys can be solution treated and aged in much the sameway as conventional heat treatable Ti alloys.

Disclosed herein is a method of making an alloy having a uniformdispersion of beta phase islands within a Ti matrix. According to thisaspect, this uniform dispersion of beta phase islands can be controlledwithin the Ti matrix by adjusting the P/M sintering time and/or bymanipulating the W powder size to a range from 8 angstroms to less then3 μm, such as less than 1 μm. The beta phase island dispersion resultsin improved room and elevated temperature properties.

In another aspect of the disclosure, the above-described method based ontungsten (W) can be used with other beta stabilizers, such as but notlimited to V, Nb, Mo, and Ta. In this embodiment, the powder size of theparticular beta stabilizer is related to the beta stabilizer'sdiffusivity at the sintering temperature of Ti.

The creation of a uniform dispersion of beta phase is dependent on,among other things, the size of the beta stabilizer powder. In oneembodiment, the beta stabilizer powder is less then 3 μm, such as lessthan 1 μm. The powder size used according to the present disclosure isalso related to the beta stabilizer's diffusivity at the sinteringtemperature. In addition, the powder size range can depend on thedesired matrix microstructure (i.e. alpha/beta or all beta), the sizeand number of beta phase islands and the desired amount of partiallydiffused beta stabilizer (residual undiffused particulate) with the betaphase islands, such as at the center of the beta phase islands.

Partially dissolved particles of the beta-stabilizing addition, such aspartially dissolved particles of W, V, Nb, Mo, or Ta, may be presentwithin, such as at the center of, the beta phase islands and maycontribute to the strengthening mechanism.

The properties of Ti metal matrix composites containing particulatereinforcement of titanium carbide (TiC), titanium boride (TiB) ortitanium diboride (TiB₂) can also be enhanced by W nanopowder additionsor the addition of sub-sieve sized powder of other beta stabilizers.

The accompanying micrograph that is incorporated in and constitutes apart of this specification, illustrates one embodiment of the inventionand together with the description, serve to explain the principles ofthe disclosure.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a scanning electron micrograph of a titanium-tungsten alloyaccording to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

One aspect of the present disclosure is directed to a composition of atitanium based alloy comprising a titanium material and tungsten in anamount ranging from 0.5% to 40% by weight. In one embodiment, the Wpowder addition used to make the alloy has an average diameter of lessthen 3 μm in size, such as less than 1 μm, and ranging from 8 angstromsto less then 1 μm as measured by the Fisher sub-screen size method,electron microscopy and/or photon correlation spectroscopy.

The titanium in the Ti/W alloy described herein may comprise CP Tipowder or a Ti alloy, such as Ti-6Al-4V.

The composition may comprise an alternative or additional slow diffusingbeta stabilizer chosen from but not limited to V, Nb, Mo, and Ta. Suchstabilizers will lead to an alloy containing dispersions of beta phaseislands or an all beta structure with dispersions of partially dissolvedbeta stabilizer. In one embodiment, the beta phase islands containundiffused particulate beta stabilizer at the core of the islands.

As described in the prior art, “beta flecks”, are generally a form ofbeta phase islands that are well-known as a defect. See, for example,“Powder Metallurgy of Titanium Alloys,” by Froes and Smugeresky, TheMetallurgical Society of AIME, Warrendale, Pa. 1980; ASM OnlineHandbook, “Wrought Titanium and Titanium Alloys—Wrought TitaniumProcessing,”; “Processing of Titanium and Titanium Alloys—SecondaryFabrication,” Y. G. Zhou, J. L. Tang, H. Q. Yu, and W. D. Zeng, “Effectsof Beta Fleck on the Properties of Ti-10V-2Fe-3Al Alloy,” Titanium 1992Science and Technology, The Minerals, Metals and Materials Society,Warrendale, Pa. 1992, Vol 1, pp513-521; andhttp://mse-p012.eng.ohio-state.edu/fraser/mse663/AlphaBeta JCW.pdf,“Properties and Applications of α+β Ti Alloys, which are allincorporated herein by reference.

The occurrence of beta fleck defects is generally unpredictable, andusually results in poor properties, and thus may lead to the prematurefailure of a component. Contrary to the teachings of the prior art, thepresent disclosure provides for the creation of uniform dispersions ofbeta phase islands that can improve the mechanical properties of Ti andits alloys. The beta fleck defect occurs in alpha-beta and near betaalloys where segregation of alloying elements results in localizedregions depleted in alpha stabilizers (e.g. aluminum) or with an excessof beta stabilizers (e.g. molybdenum). These regions then transform tothe beta phase resulting in beta flecks. Contamination of powder orcastings by tramp particles of a beta stabilizer, such as W, can alsoresult in beta flecks.

The present disclosure teaches that controlled dispersions of theso-called “beta fleck”, herein termed “beta phase islands”, can bebeneficial and improve the properties of titanium and its alloys.

In another embodiment, the alloy has a microstructure that comprisesall-alpha phase, alpha/beta phases and all beta phase, or all-alphaphase and alpha/beta phases comprising a dispersion of beta phaseislands. The beta phase islands optionally include partially diffusedbeta stabilizer within the beta phase islands, such as at the center ofthe beta phase islands.

Also described herein is a powder metallurgical method of making theabove-described composition. This method comprises:

-   -   blending a titanium material powder with a tungsten powder to        form a blended powder that comprises from 0.5% to 40% by weight        of tungsten powder having an average diameter less then 3 μm in        size, such as ranging from 8 angstroms to less than 1 μm, such        as ranging from 10 nm to 500 nm;    -   compacting the blended powder; and    -   sintering the compacted and blended powder, wherein    -   the sintered compact can then be hot isostatically pressed if        necessary.

After powder metallurgical processing as described above the part may befurther processed by techniques including, but not limited to casting,forging, and extrusion.

In one embodiment, the alloy described herein may be used in implantablemedical devices, such as orthopedic implants, including spinal implants,disc prostheses, nucleus prostheses, bone fixation devices, bone plates,spinal rods, rod connectors, knees, and hip prostheses, dental implants,implantable tubes, wires, and electrical leads. In other embodiments,the alloy may be used in drug delivery devices, including stents.

The alloy disclosed herein may also be formed into a product, such as abillet for further processing. In other embodiment, the product may bean automotive component such as valves, conrods, and piston pins.

The product may also comprise an armored vehicle component such as tanktrack center guides and undercarriage parts.

In another embodiment, the product may comprise a tool or die materialfor metal casting.

The product may also be an aircraft component such as a turbine rotor,and a leading edge of a helicopter rotor blade.

All amounts, percentages, and ranges expressed herein are approximate.

The present invention is further illuminated by the followingnon-limiting example, which is intended to be purely exemplary of theinvention.

EXAMPLE

A powder metallurgy technique was used to produce a tungsten containingtitanium alloy. Using this method, beta phase island dispersions werecreated in CP Ti and in Ti-6Al-4V with 10% by weight W. In this example,nanopowder 30 to 45 nanometers (0.003 to 0.004 μm) in size with aspecific surface area of between 7 to 10 m²/g was blended with CP Tipowder and processed as described above. These W nanopowders were alsoblended with CP Ti and master alloy powders to form the Ti-6Al-4Vcomposition shown in Table 1.

The W nanopowder was taken into solution in the Ti matrix on sinteringthe compacted blend, forming an alpha/beta structure with a uniform betaphase island dispersion.

FIG. 1 shows that the W nanopowder completely diffused to form a betaphase island dispersion in the alpha/beta matrix. The diffusion of the Wnanopowder transformed the all alpha microstructure typical of CP Ti toalpha/beta containing a dispersion of beta phase islands. In this casethere was no evidence of any undissolved W.

Table 1 shows that 10% W nano-sized powder addition substantiallyimproved the strength of CP Ti resulting in twice the strength of CP Ti,as well as a higher strength then Ti-6Al-4V with roughly equivalentductility. In the Ti-6Al-4V containing composition, the W nanopowderaddition resulted in a 30% improvement in strength while maintainingsatisfactory ductility.

TABLE 1 The Effect of 10% W Nano-sized Powder Addition on the MechanicalProperties of CP Ti and Ti—6Al—4V Ultimate Tensile Yield ReductionMaterial Strength Strength Elongation in Area Composition (psi) (psi)(%) (%) Ti 75,110 59,595 24 46 Ti + 10% W 147,320 131,515 15 37Ti—6Al—4V 137,605 124,700 14 28 Ti—6Al—4V + 10% W 178,350 171,100 9 20

Unless otherwise indicated, all numbers expressing quantities ofingredients, reaction conditions, and so forth used in the specificationand claims are to be understood as being modified in all instances bythe term “about.” Accordingly, unless indicated to the contrary, thenumerical parameters set forth in the following specification andattached claims are approximations that may vary depending upon thedesired properties sought to be obtained by the present invention.

Other embodiments of the invention will be apparent to those skilled inthe art from consideration of the specification and practice of theinvention disclosed herein. It is intended that the specification andexamples be considered as exemplary only, with a true scope and spiritof the invention being indicated by the following claims.

What is claimed is:
 1. A composition comprising a titanium alloy, saidalloy comprising tungsten in an amount ranging from 0.5% to 40% byweight of said alloy, wherein the tungsten has an average diameter lessthen 3 μm in size.
 2. The composition of claim 1, wherein the tungstenpowder has an average diameter ranging from 8 angstroms to 1 μm or less.3. The composition of claim 2, wherein the tungsten powder has anaverage diameter ranging from 10 nm to 500 nm.
 4. The composition ofclaim 1, comprising at least one beta stabilizer chosen from V, Nb, Mo,and Ta.
 5. The composition of claim 1, wherein said alloy comprisesdispersions of beta phase islands.
 6. The composition of claim 5,wherein said beta phase islands comprise undiffused particulate betastabilizer at the core of said islands.
 7. The composition of claim 1,wherein said titanium material comprises a material chosen from Tipowder and Ti alloy.
 8. The composition of claim 1, wherein said alloyhas a microstructure that comprises alpha/beta phases, all beta phases,or alpha/beta phases comprising a dispersion of beta phase islands. 9.The composition of claim 8, wherein said beta phase islands includepartially diffused beta stabilizer within the beta phase islands. 10.The composition of claim 1, further comprising at least one particulatematerial chosen from titanium carbide (TiC), titanium boride (TiB),titanium diboride (TiB₂) or combinations thereof.
 11. A powdermetallurgy method of producing a tungsten comprising titanium alloy,said method comprising: blending a titanium containing powder with atungsten containing powder to form a blended powder, said blended powdercomprising tungsten powder in an amount ranging from 0.5% to 40% byweight of said alloy, wherein said tungsten powder has an averagediameter less then 3 μm in size; compacting the blended powder;sintering the compacted and blended powder to form a tungsten containingtitanium alloy; and optionally subjecting the sintered tungstencontaining titanium alloy to hot isostatic pressing.
 12. The method ofclaim 11, further comprising subjecting the sintered tungsten containingtitanium alloy to a process chosen from casting, forging, and extrusion.13. The method of claim 11, wherein the tungsten containing powder hasan average diameter ranging from 8 angstroms to 1 μm or less.
 14. Themethod of claim 13, wherein the tungsten containing powder has anaverage diameter ranging from 10 to 500 nm.
 15. The method of claim 11,wherein the blended powder further comprises at least one betastabilizer chosen from V, Nb, Mo, and Ta.
 16. The method of claim 11,wherein the blended powder further comprises at least one particulatematerial chosen from titanium carbide (TiC), titanium boride (TiB),titanium diboride (TiB₂) or combinations thereof.
 17. The method ofclaim 11, wherein said tungsten containing titanium alloy containsdispersions of beta phase islands.
 18. The method of claim 17, whereinsaid beta phase islands contain residual beta stabilizer at the core.19. The method of claim 11, wherein said titanium containing powdercomprises a Ti powder or a Ti alloy.
 20. The method of claim 19, whereinsaid Ti alloy comprises Ti-6Al-4V.
 21. The method of claim 11, whereinthe tungsten containing titanium alloy has a microstructure thatcomprises all-alpha phase, alpha/beta phases, or all-beta phase, orall-alpha phase or alpha/beta phases comprising a dispersion of betaphase islands.
 22. The method of claim 21, wherein said beta phaseislands include partially diffused beta stabilizer within the beta phaseislands.
 23. A product comprising the composition of claim
 1. 24. Theproduct of claim 23, wherein said product is an orthopedic device chosenfrom knee, hip, spinal, and dental implants.
 25. The product of claim23, wherein said product is an automotive component chosen from valves,connecting rods, piston pins and spring retainers.
 26. The product ofclaim 23, wherein said product is an military vehicle component chosenfrom tank track, suspension, and undercarriage parts.
 27. The product ofclaim 23, wherein said product is a tool or die material for metalforming chosen from shot sleeves, plungers and dies.
 28. The product ofclaim 23, wherein said product is an aircraft component chosen from aturbine rotor, and a leading edge of a helicopter rotor blade, tubing,valves and fittings.
 29. The product of claim 23, wherein said productis a billet for subsequent casting, forging or extrusion.
 30. A powdermetallurgy method of producing a titanium containing product, saidmethod comprising: blending a titanium containing powder with a tungstencontaining powder to form a blended powder, said blended powdercomprising tungsten powder in an amount ranging from 0.5% to 40% byweight of said alloy, wherein said tungsten powder has an averagediameter less then 3 μm in size; compacting the blended powder; andsintering the compacted and blended powder, said method optionallycomprising a post-sintering process chosen from hot isostaticallypressing, casting, forging and extrusion.
 31. The method of claim 30,wherein said product is an orthopedic or dental implant.
 32. The methodof claim 30, wherein said product is a billet that is subjected to atleast one post-sintering process chosen from casting, forging, andextrusion.